1. Field of the Invention
The present invention relates to a superconducting material having a critical temperature of 90 K. or more and a method of producing the same.
2. Description of the Prior Art
A superconductivity is a phenomenon in which a certain kind of electrically conductive substance shows an electrical resistance of zero when it is held at low temperatures near an absolute temperature of zero. Nb.sub.3 Sn having a critical temperature of 18 K. has been known as a representative one. And, its applications in the following fields are thought.
(1) Lossfree transmission of electricity via a transmission line;
(2) Plasma-confining coil in a nuclear fusion;
(3) Coils for floating and propelling a linear motor car;
(4) Coils for propelling an electro-magnetically propelled ship;
(5) Coils for generating a magnetic field and detecting signals in the magnetic resonance imaging;
(6) Coil for regulating an orbit of particles of a beam line and a detector of reacted particles in a particle accelerator;
(7) Josephson's device for a superhigh speed computer; and
(8) Fine magnetic detecting coil for a magnetic brain wave meter and a magneto-cardiograph.
However, in order to maintain the superconducting state it is necessary to maintain the substance at temperatures near an absolute temperature of zero and liquid He (having a boiling point of 4 K.) capable of achieving the above described requirement is expensive, so that the application of the superconducting material mentioned above is wanting in reality. Thus, the investigation and development of a substance showing a superconductivity at higher temperatures have been carried out. At the beginning of the 1970's Nb.sub.3 Ge having a critical temperature of 23.9 K. was discovered. Thereafter, no developement has been obtained about 10 years but in April in 1986, IBM Corp. published that a compound comprising La, Ba and CuO has a critical temperature of 30 K. In addition, in December in 1986, University of Tokyo published a superconducting material having a critical temperature of 37 K., the Bell Institute of ATT published a superconducting material having a critical temperature of 40 K., and the Electrotechnical Laboratory in Japan published a superconducting material having a critical temperature of 54 K. in January in 1987. It is said that the last one is a compound comprising La, Sr and CuO. In order to maintain a substance having a critical temperature of such degree under the superconducting state liquid hydrogen (having a boiling temperature of 20 K.) and liquid neon (having a boiling point of 27 K.) can be used, and thereby, its application to various uses became realistic. However, in view of the economy, a substance capable of maintaining the superconducting state by cooling inexpensive liquid nitrogen (having a boiling point of 77 K.), that is, concretely speaking, a substance having a critical temperature of 90 K. or more, is required and its development and discovery have been expected.